Alkylation of benzene produces alkylbenzenes that may find various commercial uses, e.g., alkylbenzenes can be sulfonated to produce detergents. Alkylbenzenes are produced as a commodity product in large-scale facilities, e.g. often in amounts of 50,000 to 200,000 metric tonnes per year per plant. In the alkylation process, benzene is reacted with an olefin the desired length to produce the sought alkylbenzene. The alkylation conditions comprise the presence of homogeneous or heterogeneous alkylation catalyst such as aluminum chloride, hydrogen fluoride, silica alumina or zeolitic catalysts and elevated temperature.
The alkylbenzene must meet stringent product specifications to be commercially acceptable. For instance, alkylbenzenes, to be desirable for making sulfonated surfactants, must be capable of providing a sulfonated product of suitable clarity, biodegradability and efficacy. The benzene content of the product should be relatively free from benzenes, e.g., less than about 1 part per million by weight (ppmw), and often less than about 0.5 ppmw. Additional considerations for commercial alkylbenzene products include the 2-phenyl content and linearity of the alkyl substituent.
An important property of alkylbenzene as a feed for making a sulfonated surfactant is that it not impart undue color to the sulfonated product. Thus, the alkylbenzenes should have an absence of color formers, or color bodies. Color bodies are components that impart color to the alkylbenzene. Saybolt color is one procedure for determining color of a liquid and for purposes herein refers to ASTM D-156-00, Standard Test Method for Saybolt Color of Petroleum Products (Saybolt Chronometer Method), which is in effect on Jul. 31, 2004, available from ASTM International. Desirable alkylbenzenes have a Saybolt color of at least +25, and preferably at least +29.
In the process for making alkylbenzene using a solid, acidic catalyst, benzene is alkylated with an olefin under alkylation conditions. A high benzene to olefin ratio is used in part to reduce side reactions that generate heavies and in part to serve as a heat sink for the alkylation reaction. Typically, alkylbenzene is purified by the use of several distillation steps. For instance, see Pujado, Linear Alkylbenzene (LAB) Manufacture, Handbook of Petroleum Refining Processes, Second Edition, pp 1.53 to 1.66 (1996), especially pages 1.56 to 1.60. In general, the alkylation reaction product is subjected to a first distillation in a benzene column to separate benzene as an overhead stream that can be recycled to the alkylation reaction. The bottoms stream from the benzene column is then subjected to a distillation to separate paraffins and unreacted olefin in a paraffins column. The paraffins-containing overhead is capable of being recycled to a paraffin dehydrogenation unit while the bottoms stream is passed to a heavy alkylate distillation column. In the heavy alkylate distillation column, heavies are separated from the lighter alkylbenzene, and a heavies-containing stream is withdrawn as a bottoms stream. If desired, the bottoms stream can be subjected to a further distillation to recover additional alkylbenzene.
Benzene also finds other applications in an alkylbenzene complex. For instance, the solid, acidic catalyst must be periodically regenerated. The regeneration is effected by passing benzene over the catalyst at elevated temperature to remove deactivating components. Another use for benzene is where the olefin-containing feed is subjected to selective sorption to remove unwanted aromatic compounds, and benzene is used to regenerate the selective sorbent. See, for instance, U.S. Pat. No. 6,740,789. If the alkylbenzene complex provides for transalkylation of heavies over a solid catalyst, then benzene may also find use in regenerating the transalkylation catalyst.
Efficient use of benzene is required for commercially viable alkylbenzene complexes. Thus, benzene must be recycled. Proposals have been made to effectively use the benzene by cycling it through two or more unit operations in the alkylbenzene production complex. See, for instance, U.S. Pat. No. 6,740,789. Hence benzene management in the alkylbenzene production complex involves not only the alkylation reaction but also a plurality of other uses. Typically, therefore, spent benzene from such regenerations is returned to the benzene column for the purification of crude alkylbenzene. The benzene column, together with make-up benzene, provides benzene for the alkylation as well at the regeneration uses.